1) Field of the Invention
The present invention is directed to optical lenses formed by the selective concentration of particles in a liquid by acoustic pressure.
2) Description of Prior Art
Solutes can be concentrated in a liquid using externally-applied acoustic pressure, for example from ultrasonic wave generators. These solutes include particles suspended in the liquid. In addition, the optical index of refraction of a liquid can be changed by changing the particle distribution in the liquid.
U.S. Pat. No. 6,216,538 (Yasuda et al.) discloses an apparatus for handling particles in a fluid using acoustic radiation pressure. A method is provided that makes it theoretically possible to fix some types of particles at any position and to move and transport in any direction with any speed. Ultrasonic wave generating elements are focused in any position, and a force potential wall is produced at this focal point. The force potential at the focal point varies depending upon the densities of both water and the particles. For lighter particles such as polystyrene, the force potential has a minimum value at the focal point, and those particles are collected or concentrated at the focal point. For particles such as lead and iridium, the force potential takes a maximum value at the focal point, and those particles are repelled or move away from the focal point.
In order to change the optical index of refraction of a liquid such as water, heavier or denser particles need to be concentrated at the focal point. Therefore, an acoustically-focused optical lens is needed that concentrates the heavier particles at a point in the liquid to achieve the optical lens for desired use. Such particles will concentrate at or near nodes or nodal lines. The invention, as described below generates a node at the center for a greater concentration of particles.